1. Technical Field
The present invention relates to an optical filter, a method of manufacturing an optical filter, an optical instrument, and the like.
2. Related Art
JP-A-2009-134028 describes an optical filter which is constituted by a Fabry-Perot Etalon filter (hereinafter, referred to as an Etalon filter or simply referred to as an Etalon) having a pair of optical films arranged to face each other at a predetermined gap.
The Etalon filter described in JP-A-2009-134028 has a first substrate and a second substrate which are arranged in parallel with each other, a first optical film (first reflecting film) which is formed on the first substrate, and a second optical film (second reflecting film) which is formed on the first substrate to face the first optical film at a predetermined gap. Each of the first optical film and the second optical film forms a mirror, such that only light in a predetermined wavelength band based on the length (gap amount) of the gap can be transmitted through multiple interference of light between mirrors. By variably controlling the gap amount, it is possible to switch the wavelength band of light to be transmitted.
In the Etalon filter described in JP-A-2009-134028, in bonding the first substrate and the second substrate to each other, bonding films containing siloxane (Si—O) bonds is used. The precision of wavelength separation in the Etalon filter is deeply involved in the precision of the gap amount. Accordingly, in order to improve the performance of the Etalon filter, it is necessary to control the length of the gap between the first optical film and the second optical film with high precision.
In order to realize the improvement in wavelength resolution while promoting reduction in the size of the Etalon filter, there is a need for a technique which controls the gap between the first optical film and the second optical film, for example, in a nanometer order with high precision. Accordingly, when the first substrate and the second substrate are bonded to each other through bonding films containing siloxane bonds, it is important to secure the parallelism between the substrates without inclining the substrates.
However, in order to bond the substrates to each other using bonding films, for example, it is necessary to activate the bonding films formed on the substrates by ultraviolet irradiation, oxygen plasma treatment, or the like, to carry out positioning (alignment) of the substrates, and to apply a weight to the substrates. During this process, slight inclination may occur on the substrates.
As the factor for the occurrence of inclination on the substrates, for example, there is misalignment (bonding film misalignment) when partially forming bonding films on the substrates or substrate misalignment in a process for bonding the substrates to each other. A slope or roundness is likely to be formed in the edge portion of the bonding film. This also becomes the factor for the inclination of the substrates.